In the four copending applications above there are disclosed functionalized congeners of N.sup.6 -phenyladenosine and 1,3-dialkyl-8-phenyl xanthine and in which a spacer chain terminating in a chemical functional group is inserted at the para position of the phenyl for the purpose of enhancing the binding properties of the functionalized congener to the A-1 adenosine receptor site or the A-2 adenosine receptor, depending upon the drug properties of the drug portion or primary pharmacophore of the molecule. In the case of adenosine the pharmacophore is an agonist. In the case of xanthine the pharmacophore is an antagonist. Both adenosine and xanthine derivatives bind competitively to A-1 and A-2 adenosine receptors.